Welding transformer control system



Patented Oct. 25, 1949 WELDING TRANSFORMER CONIROL SYSTEM Didier Jumeaux, Wauwatosa, Wis., asignor t0 Allis-Chalmers Manufactuflng Company, Milwaukee, Wis., a corporation of Dclaware Application April 24, 1946, Serial No. 664,567

4 Claims. 1

"This invention relates in general to improvements in control systems for welding transformers, and more particularly to means for automatically rendering a welding transformer inoperative when the associated welding circuit becomes short circuited or open circuited.

The supply of alternating current to welding electrodes is frequently efiected through a transformer having a secondary open circuit voltage of suflicient magnitude to subj ect an operator touching bath electrodes simultaneously tu shock or to greater hazards. The transformer may also be seriously damaged if the secondary winding thereof remains short circuited for a considerable length of time. It is therefore desirable to rentier the transformer inoperative whenever the associated welding circuit is idle or short circuited. The means provided to perform the latter functian may comprise different arrangements of switching devices, such as contactors and relays, which are provided with operating coils. T0 insure that the welding transformer does not accidentally become reconnected for normal operation in response to burning out of an actuating coi], it is advantageous to 50 design the system that such operative connection requires all actuating coils to be supplied with current.

In a preierred embodiment of the invention, the actual voltage of the welding circuit is compared with a voltage equal to the secondary open circuit voltage of the welding transformer through connections comprising an inductive voltage diVider for detecting the actual condition of: the'welding' circuit. 'To reduce thecost and complication ofthe system to the greatest possible eitent; the coil' controlling the closing operation of'-the cdntact0r'Switch for the welding transfirmerand the oeil of a relay for causing opening: of the contactdrswitch upon short circuiting of the welding circuit may form the principal elements of the voltage divider.

It is therefore an object of the present invention to provide an improved system for rendering a welding transformer inoperative when the associated welding circuit 15 idle or open circuited, in which burning out of the actuating coi] of any switching device will prevent operative connection of the transformer.

Another object of the present invention is to provide an improved system for rendering a welding transformer inoperative when the associated welding circuit is idle or short circuited, in which the desired Operati0n is obtained by the use of only two switching devices.

" Obiects and advantages other than those above set forth will be apparent from a consideration of the following description when read in connection with the accompanying drawing, which diagrammaticaily illustrates one embodiment of the present invention.

Referring more particularly to the drawing by characters of reference, numeral 6 designates a welding transformer provided with a primary winding Sa and a secondary winding 6?). The secondary winding is connected with a welding circuit 17 for supplying current t0 a pair of electrodes 8*, 9. Electrode 8 is assumed to be a rod of weld metal, and electrode 9 the work to be welded. The fiow of current through electrodes 8, 9 is adjustably limited by causing the path of the current flowing through winding 6a or through winding Bb to have a substantial impedance. The latter result may be obtained by 50 disposing windings 6a, 6b as to cause the leakage reactance thereof to have a substantial value or by connecting winding 6b to circuit 1 through impedance means such as an adjustable reactor l I of any suitable type.

Winding 6a is to be Connected with a suitable source of current such as a circuit l2 energized from a suitable generator (not shown) through connections including the main contacts l3b of a contactor switch [3. Closing operation of switch 83 is controlled by means of an inductive actuating coi] 8311 which preferably actuates the armature of switch [3 directly, although such actuation may also be efiected through the intermediary of a relay. Coil I3a is energized from an auxiliary transformer l4 provided with a primary winding l4a connected across circuit [2. The secondary winding l4b of transformer M is an undivided winding having an open circuit voltage substantiaily equal to the open circuit voltage ,of winding 6b. -Means comprising coi] l3a connect winding I4b across welding circuit 1 to cause closure cf switch I3 in response to increase of the voltage impressed on coi] l3a upon momentary short circuiting et circuit 1, and to cause opening of switch 13 in response to open circuiting of circuit 1. Switch 13 preferabiy operates instantaneously to close contacts I3b. The speed of opening of contacts l3b may however be adjusted to any desired extent by proper choice of the elements of switch l3, which may include any suitable known delaying means convention- 'ally represented as a dashpot l3e.

A delayed relay l5 is provided for opening the circuit of coi] la tu cause opening of switch l3 in response to short circuiting of circuit 1. The actuating coi1 I5a of relay l5 may be inserted in a,4ae, ms

either confiection between coil Ila and the two conductors et circuit 1. In the present embodiment. coil "la is connected between coil I la and the conductor et circuit 1 connected to electrode I, and coil Ila accordingly also forms part of a shunt circuit connecd acroas circuit 1. Contacts Ilb of relay Il are inserted in one of the connections Joining coil Ila with winding Ilb and with circuit 1. Relay Il may be provided with a dashpot Ilc or other suitable means for causing contacts Ilb to close instantaneously and to open with a predetermined time delay.

As a result 015 the connections above set forth. inductive colis lia, Ila constitute elements of an inductive voltage divider connected across winding Ilb, circuit 1 being connected across only 8. portion of the voltage divider consisting of coil Ila for causing selective energization of coil Ila in dependence upon the magnitude of the voltage of circuit 1. Coil Ila is so dimensioned as to cause switch Il to remain in the position shown as long as circuit 1 is energlzed only from transformer Il through coil I la, and to cause switch Il to close contacts I3b in response to momentary short circuiting of circuit 1. To allow greater latitude in the choice of coil Ila, a resistor Il bridged by contacts Ild oi switch Il may be connected in series with coil lia. The voltage divider further comprises a suitable impedance device, such as a resistor l1 connected in parallel with resistor Il, coil lla, and contacts Ilb for energizing circuit 1 and coil Ila prior to closure of contacts I5b. To reduce the amount of energy dissipated in the voltage divider, the connections thereof may be modified in response to operation of switch Il opening contacts llc connected in series with resistor I1.

In operation, circuit Il being energized and switch Il being in the position shown, winding la does not receive current from circuit I2. Winding Ila, however, is energized irom circuit I! and a voltage equal to substantially the normal open circuit voltage of winding lb is impressed from winding Ilb on contacts Ilc, resistor I1 and circuit 1. A predetermined reduced voltage is thus impressed on circuit 1 and on coil Ila, and relay Il closes contacts Il?) te connect coil I3a and resistor I l between circuit 1 and winding lib. The flow of current through coil Ila causes the voltage impressed on circuit 1 to rise, but the elements of the system are so chosen that the voltage of circuit 1 does not reach such a value as to constitute a substantial hazard to human life. The voltage then impressed on coil Ila is insufllcient to cause operatien of switch Il.

Welding operation may be initiated by momentarily bringing electrode I in contact with electrode 0. Circuit 1 is thereby momentarily short circuited, and the. full voltage of winding Ilb is impressed on coil Ila and resistor Il. Switch Il closes contacts Ilb, which connect winding la with circuit I2, and opens contacts Ilc to prevent further dissipation of energy in resistor I1.

Electrodes l, 9 may then by separated to draw a welding arc therebetween. Circuit 1 is then malnly supplied with current from transformer l, and the fiow of current from winding lb through reactor Il malntalna the voltage of circuit 1 within a limited range of values substantial1y lower than the open circuit voltage of winding lb. Relay Il maintains contacts Ilb cled as longas the voltage of circuit 1 retains a. substantiel value. Tire voltage impressed on coil Ila through contacts Ild and Ilb remains 4 sufflcienfly high to cause switch Il to maintain contacts Ilb closed.

When the welding arc Is intermnd by separatien et electrodes l, I beyond a predetcrmined distance, the flow of current through winding lb and reactor Il decreases to a negligible value. Winding lb then impresses on circuit 1 substantially the full open circuit voltage thereoi. which ls equal to the voltage oi' winding Ilb. The two terminais of coil I8a then being at substantiaily the same potentiai, the coil is without apprcciable current and switch Il opens contacts Ilb to disconnect winding la from circuit Il. Circuit 1 is then again energized at reduced voltage from winding llb, and another welding operation may be initiated by engagement et electrodes l. l.

If electrodes I, 9 are held in contact for a substantlal length of time, swifch Il flrst closes contacts Ilb in the manner above set forth. After a predetermined length of time, relay Il retums to the position shown, thereby opening contacts Ilb and deenergizing coil Ila. Winding la la disconnected from circuit I: and the welding electrodes are supplied with current of negiigible value from winding Ilb through resistor I1. Upon subsequent separation of electrodes l. l, relay Il recloses contacts Ilb to prepare the system for initiation of another welding operation.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letterc Patent:

1. In a control system for a welding transformer comprising a primary winding to be connected across a source of alternating current and a secondary winding connected to a welding circuit, the combination of a switch for connecting said primary winding with said source, an actuatin coil for controlling closing operation of said switch, an auxiliary transformer connected to said source and provided with a secondary winding, said welding transformer when energized from said source having a. secondary terminal voltage which upon open-circuiting of said welding circuit substantiay equals the open circuit voltage of said auxiliary transformer secondary winding, and means comprising said coil connecting said auxiliary transformer secondary winding across said welding transformer secondary winding to cause closure of said switch in response to an increase in the current through said coil upon short-clrcuiting of said welding transformer secondary winding and to maintain said switch closed by the diiierential eflect of the said voltages on said coil, said switch being blased to open in response to deenergization of said coil upon open-circuiting of said welding circuit substantiaily equalizing the said voltages.

2. In a control system for a welding tramformer comprising a primary winding to be connected across a source of alternating current and a secondary winding connected to a welding circuit. the combination of a switch for connecflng said primary winding with said source. au actuating coil for controlling cloaing operation of said awitcb. an auxiliary transformer connected to said source and provided with a secondary winding. said welding transformer when energlzed from said source having a aecondary terminal voltage which upon open-circulting of said welding circuit substanflally equals the open circuit switch closed by the diflerential effect of the said voltages on said coil, said switch being biased to open in response to deenergization of said coil upon open-circuiting of said welding circuit substantially equs'lizing the said voltages, said means including delayed means responsive after a predetermined period to a prolongd decrease in the terminal voltage of the welding transformer secondary winding upon prolonged short-circuiting of said welding circuit for opening the circuit of said coil after the circuit of said coil has been closed by the diflerential effect of said voltages on said coil.

3. In a control system for a welding transformer comprising a primary windingfo be connected across a source of alternating current and a secondary winding connected to a welding circuit, the combination of a switch for connectin8 said primary winding with said source, an actuating coil for controlllng closing operation of said switch, an auxiiiary transformer connected to said source and provided with a secondary winding, said welding transformer when encrglzed from said source..having a secondary terminal voltage which upon open-circuiflng of said welding circuit substantfally equals the open circuit voltage of said auxiliary transformer secondary winding, and means comprising said coil connecting said auxiliary transformer secondam winding across said welding transformer secondary winding to cause closure of said switch. in response to an increase in the current throfl8h said coil upon short-circuiting of said welding transformer secondary winding and to malntain said switch closed by the diflerential effect of the said voltages on said coil, said switch being biased to open in response to deenerglzation of said coil upon open-circuiting of said welding circuit substantiafly equalizing the said voltages, said means including delayed means comprising the combinatlon of a delay switch with instantaneous closure and 'time-delayed opening for 'connecting said coil between said auxiliary transformer secondary winding and said welding transformer secondary winding, a solenoid coilv con-V nected across said welding circuit for controlling closing operation of said delay switch, said solenoid coil being effective to close said delay switch in response to energization of said auxiliary transformer and to maintaln said delay switch closed durlng welding operatlon of said welding transformer, said delay switch being biased to open in response to a prolonged decrease in the voltage of the welding circuit upon prolonged short-circuiting of said weldlng circuit.

4. In a control system for a welding transformer comprising a primary winding to be connected across a source of alternating current and a secondary winding connected to awelding circuit, the combination of a switch having a plurality of sets of contacts, one of said sets of contacts being operable for connecting said primary winding with said source upon closing operation of said switch, an actuating coil for controlling closing operation of said switch, an auxiliary transformer connected to said source and provided with a secondary winding, said welding transformer when energized from said source having a secondary terminal voltage which upon open-circuiting of said weldlng circuit substantially equals the open circuit voltage of said auxiliary transformer, means comprisins said coil connecting said auxiliary transformer secondary winding across said welding transformer secondary wlnding to cause closure of said switch in response to an increase in the current through said coil upon short-circuiting of said welding transformer secondary winding and to maintain said switch closed by the diflerential effect of the said voltages on said coil, said switch being biased to open in response to deenergization of said coil upon open-circuiting of said welding circuit substantiaily equalizing the said voltages, and a shunt circuit comprising impedance means connected across said coil for controlling the voltage impressed on said coil, another of said sets of contacts being operable to open saidshunt circuit in response to closing operation of said switch.

REFERENCES CITED The following references are of record in the file of this patent:

ummn srsfls PATENTS Number Name Date 2,110,438 Candy Mar. 8, 1938 2,189,606 King Feb. 6, 1940 2,214,868 Welch Sept. 17, 1940 2,364,372 Kenrick Dec. 5, 1944 2,376,215 Welch May 15, 1945 

